Problem compiling trunk from github: MissingRequirementError: class scala.reflect.BeanInfo not found.

I have a fork of [https://github.com/scala/scala] which until
yesterday has been building ok with "ant". Then recently I git pulled
and started getting the following error during stage "quick.lib":

[scalacfork] error: scala.reflect.internal.MissingRequirementError:
class scala.reflect.BeanInfo not found.

It doesn't appear related to my changes. Has anyone else had this
problem? Any suggestions on how to resolve or what it means?

Thanks
Ben